With his recent victory over Guiche, Saito has become semi-popular among the commoners and several nobles. Kirche in particular has chosen him as her next boyfriend. In a devious plan, she attempts to seduce him, although this fails when Louise finds out. Annoyed by Saito's lack of defenses, Louise drags him out to town to pick up a sword after considering his hidden talents. Kirche, unwilling to let go so easily, matches Louise's gift with a more impressive sword. Of course, it simply causes more problems between Saito and Louise.

The lovey-dovey antics of Louise under the love potion persist to the point of freaking Saito out. In desperation, Saito demands that Montmorency create an antidote. She refuses to do so until Saito learns of the illegality of creating love potions and threatens her with possible arrest. As the antidote requires the tears of a water elemental, Montmorency leads Saito and Louise to Lake Lagdorian. There, they find Kirche, Tabitha, and a whole new problem.

Eléonore drags Louise, Saito, and Siesta back to the Vallière house, where Louise is announced to be engaged to a duke. Saito goes to talk to her at night but instead finds her sister who beats him like Louise does. Saito confesses his true feelings to Louise, makes out with her in a childhood boat, fights his way out of the Vallière residence, and heads back to school with Louise. She doesn't believe him about what happened in an earlier incident and beats him again while Siesta tells herself she is the only one for Saito.

Henrietta is convinced to sign a declaration of war against Albion. News of a victorious battle for the Tristain and Germania allied forces reaches a town that Louise and Saito are currently in. Saito discovers a sailor uniform on sale at a clothes merchants shop, and buys it, opting to give it to Siesta rather than to Louise. Upon returning to the academy, the two join Agnes and Julio on exploring a secret archive hidden beneath the school, which Agnes was denied permission. Agnes wishes to obtain the information there regarding her home town of D'Angleterre's burning to help carry out her revenge against those involved. Eleonore is picked to open to lock to the entrance. As the group heads farther down, they are joined by Siesta, who is wearing the sailor uniform Saito gave her earlier. After discovering that Saito gave the sailor uniform to Siesta because Louise lacked the chest size to make it look good, Louise blows a part of the cave in the way they came. With little to do but move further, the group finds the archives and are sent to look for the records regarding the town of D'Angleterre's burning 20 years ago. When Siesta trips and makes a mess of the books, Eléonore returns them to their proper place with magic, which triggers the archives' security system and begins to bring the bookshelves to a close. Agnes finally finds the information regarding D'Angleterre's burning, but a part of the page that lists the person who led the attack is missing. The group narrowly escapes the collapsing of the bridge that led them to the archives. Upon realizing that Louise had blocked their way out from before, Julio grants Saito permission to have intimate moments with Siesta. Siesta is happy to oblige and Saito also thinks it to be a good idea, however, Louise is watching and is preparing to blow something else up. When Saito points out that the cave in she made earlier is in the opposite direction, Louise tells him to shut up and blows them up anyway.

Tiffania travels back to Tristain with the group. While introducing herself to the Queen, she forced to remove her hat revealing a pair of long, pointed elf ears. Elves are shunned by civilized society, and she explains that she is in fact a half-elf. Her mother was an elf that passed away years earlier, and her father was the archduke of Albion and Henrietta's uncle. As the Queen, Saito, Louise, Agnes, and Tiffania discuss the whereabouts of the other void user(s), Henrietta offers to knight Saito again and he accepts. Henrietta also appoints Siesta as Saito's servant, much to Louise's frustration. Saito, Louise, and Siesta arrive back at the academy by dragon to a huge celebration in Saito's honor lead by the self-proclaimed Knights of Ondine, a group of students at the academy captained by Guiche.

It starts off with Siesta at the imp cafe with her uncle and cousin, Jessica, telling her to try harder at getting Saito, eventually giving her a love potion. After the credits, it goes to Saito and Louise’s room where Siesta is cleaning and contemplating using the potion on Saito when Louise comes in dragging Saito who is tied up behind. This causes a fight between Louise and Siesta about the treatment of Saito. Finally, Siesta who believes that she can take better care of Saito than Louise is allowed one hour for that purpose. When the two of them get to Siesta's house she decides they should play newlyweds but after several chances she finally decides to use the potion only to drop it out the window where it is found by Montmorency who imeadietly identifies it as a love potion but accidentally inhales it and the first person she looks at is Louise who has come to check up on Saito, but after Montmorency kisses her it is discovered the potion is more like a virus and it is eventually left for Tiffania to sort out. Tiffania uses a long-forgotten spell to wipe the memories of all those affected by the charm, and Montmorency forgives Siesta for causing the mess, reminding her not to do it again. Tabitha is later confronted by Sheffield, who attempts to sway the young girl by tempting her with promises to save the former's mother.

Using her talents at persuasion, Kirche discover that Tabitha is being held in Al Hambra. Upon arriving in Al Hambra, the gang decide upon a plan of attack. Under the pretext of having a show, they will make the soldiers drink alcohol laced with sleeping potion. When Kirche doesn't assign anything to Louise, she gets angry and demands to be given something to do. Kirche reveals that she knows the Louise is a void mage, and apologises for her past behaivor, and invites her over to Germania. Later on, Derflinger advises Saito to say something to her, saying that Void magic is dependant on emotional strength. Saito decides to do so, and finds her posing in front of a mirror in a dancing costume. Louise begins to tempt Saito, and Saito pushes her onto the bed, but they are interrupted by Guiche. In Tristan, Agnes frees Colbert. She saids that she cannot forgive him for burning her village, but has a chance to end the cycle of hatred that would erupt should she kill Colbert. Back in Al Hambra, the Baron wants Louise to attend to him personally, and she agrees, planning to drug his wine, but discovers that the sleeping potion slipped out of her bra. Saito and Tifa discovers the bottle and go to rescue Louise, Tifa using her magic to wipe the Baron's memories. Having drugged all the soldiers, they encounter Bidashal, who easily defeats all their attacks using Counter. Derflinger tells Louise to cast Dispell on him, which she does, allowing Saito to break through Bidashal's Counter. Tifa stops Saito from killing Bidashal, who tells them where Tabitha is and lets them go, and warns them that Joseph is a cold blooded man, and that it wouldn't end there. Tabitha is awakened by Slyphid, and cries upon seeing the gang, even as Sheffield spies on them using her butterfly.